Human sperm reaches the fallopian tube and fertilizes the egg. Generally speaking, theyA distance of 15cm to 18cm needs to be moved.Considering that sperm is one of the smallest cells in animals -The length of human sperm from acrosome to end is only about 50 microns., moving more than 15 cm is not an easy task.
In fact, not only is the distance very far for sperm, there are also various "booby traps" on the 15 cm journey, because sperm is a foreign body to women and will be naturally defended against it.
These include cervical mucus trapping sperm, white blood cells engulfing sperm, etc. When hundreds of millions of sperm set off at the same time each time, only about 200 can actually reach their destination - contacting the egg.
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So the interesting question is, how do sperm move? How does it obtain energy to keep pushing forward?
There are some very interesting stories about the "swimming" of sperm, so it must be mentioned separately. This thing has fooled scientists for more than 300 years.
How Sperm Deceived Scientists for Over 300 Years
In 1677, after the Dutch scientist Leeuwenhoek, the father of optical microscopy, improved the microscope, he carefully observed his own sperm through this microscope. This was the first time that humans saw sperm.
Picture: Leeuwenhoek
According to Leeuwenhoek's description, he saw a huge number of "microorganisms". Each of these "creatures" had a swollen head and a long, almost transparent tail. They were full of energy, squirming like snakes, and like eels in the water.
At that time, people did not think that these were human germ cells. In fact,Leeuwenhoek believed that they were a kind of parasitic animal (probably he was frightened when he first saw these of his own), and specifically created a term "spermatozoa" (now translated as sperm animal) to describe this "creature".
Picture: At that time, people thought that there were little people living in the acrosome of sperm.
For a long time after the discovery of sperm, people actually didn't know what these cells were used for.
In 1695, Nicholas Hartsock, also a Dutchman, after observing sperm, he instantly felt that he had understood the "secret of God". He defined the role of sperm for the first time, believing that there were little people living in the sperm, and then these little people developed into larger people in the woman's belly. This is what fertility is all about.
But the embarrassing thing is that this man can't explain why so many people went in but only one or two came out in the end.
People didn't understand the secrets of mammalian reproduction until 1827, because that year scientists discovered eggs (it was difficult to find eggs because their number was very limited). It was not until 1876 that scientists finally observed the fusion of sperm and eggs, and the secrets of mammalian reproduction were finally clear.
Let's go back to Leeuwenhoek's discovery of sperm. Although he didn't know what these "creatures" were for, he was definitely very good at describing the creatures under the microscope.
In that era before cameras, Leeuwenhoek even drew a portrait of sperm by hand (pictured above), and for the first time described through images and words at the same time how sperm moves - it moves itself forward by flicking its tail left and right like a tadpole or fish.
Sperm moving in this form (wiggling tail) probably fits the stereotype of almost all of us, because this is usually how it is described in most of the popular science books we come into contact with.
Until recently (2020), researchers from the National Autonomous University of Mexico discovered that,It turns out that sperm does not "swim" by swinging its tail like this. It actually moves in the form of a rotating hole.
Researchers from the National Autonomous University of Mexico used a 3D microscope with a piezoelectric device and a high-speed camera capable of recording more than 55,000 frames per second to 3D scan free-swimming sperm, and then mathematically constructed the movement of the sperm (as shown below) [1]
This study was published in the journal Science Advances on July 31, 2020. Its researcher Gadêlha said in an interview: The sperm does not swim at all, it just keeps drilling into the liquid.
In fact, due toRapid and highly synchronized rotation of sperm - 20 rotations per second, observing with a 2D microscope cannot correctly understand their movement - you can only see left and right swings, and modern research usually uses 2D microscopes, so sperm have been fooling scientists like this for more than 300 years.
Why does sperm spin?
Sperm are highly specialized cells, which means they are under tremendous evolutionary pressure, and all their characteristics have a single purpose, which is to complete fertilization.
The swimming posture of swinging from side to side is suitable for propelling in some easy-to-swim liquids, and the environment that sperm needs to face to complete fertilization is very complex.
On the same journey, they all need to face a variety of environments, sometimes it is sticky and cannot be propelled at all, sometimes it is lubricated, and sometimes it is simply dry, so spinning like a top is much better than swinging propulsion.
In addition, this study also found that the tail of human sperm is actually unbalanced and only swings on one side, which means that it should be spinning in circles due to the one-sided swing.
butSperm have found an adaptation. They roll as they swim, and the acrosome also rotates in the direction of the tail rotation. This way can offset the asymmetry caused by the unilateral swing.
I reviewed a study in 2019 and found that the acrosome of mammalian sperm is spiral-shaped, like a screw [2], which is exactly in line with the movement of sperm.
So, there is another question. Since sperm are so small and they have to drill holes so hard, where do their energy come from?
In fact, this is also part of the highly specialized nature of sperm.
We know that the energy for cell activities mainly comes from mitochondria, which are called energy factories of cells. Although sperm are small in size, they have a lot of mitochondria, which are like small batteries that supply energy to sperm.
These mitochondria are concentrated in the middle part of the sperm, and in order to make full use of space, scientists found that these mitochondria are spiral-shaped.
What provides "fuel" to these mitochondria is their activity site. Only there they have a chance to survive for more than 5 days, while in other environments sperm will be quickly inactivated.
Finally, let’s talk about a widely spread misconception about sperm.
Many of us have heard that only the fastest sperm has a chance to complete fertilization, so each of us has won once among hundreds of millions of competitions since birth.
But this is not actually the case,More and more evidence has shown that the fastest running (or drilling) sperm will only encounter the egg first, and the egg has the final choice. They will choose one from hundreds or even thousands of sperm that complete the race [3].
refer to:
[1].https://doi.org/10.1126/sciadv.aba5168
[2].https://doi.org/10.1098/rstb.2019.0149
[3].https://www.news-medical.net/news/20200611/The-egg-decides-which-sperm-fertilizes-it.aspx